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Epidemiology of cancer and influencing factors
Before the mid 19th century the common view among physicians were cancers being foreign bodies that took root in the body 1. However, this notion was challenged when histology as a developed, revealing that cancer cells were simply a mass of cells with organization similar to body tissue albeit more haphazard 2. This led to the idea of cancers being more prevalent in certain populations due to factors such as the environment and genetics. Thus, the idea of epidemiology, the study of the distribution and factors influencing diseases within a certain population, was born. With these discoveries, the postulations of surgeons, such as Percivall Pott from 1775, showed that certain cancers were more prevalent in those performing specific jobs. Pott noticed that Chimney sweeper’s cancer, a form of squamous cell carcinoma, occurred much more frequently in chimney sweepers than the local population 3; hence the name. Chimney sweepers work in the presence of soot, later determined to be carcinogenic; but those in the UK did not have protective equipment sometimes even working naked leading to increased exposure to soot 4. However, on the continent, German chimney sweepers wore tight fitted clothing, as shown by Fig. 1, preventing soot accumulation on the surface of the scrotum 5. This meant rates of Chimney sweeper’s cancer among British chimney sweepers were much higher than the German counterparts. The cancer also only affected chimney sweepers who have been in the profession since a young age with the median age of onset of symptoms at 37.7 years and cases of boys as young as 8 years old demonstrating symptoms 6. By showing that increased incidence of cancer due to soot exposure Pott effectively spurred the idea of epidemiology. This was the first record showing a correlation between cancer and an environmental factor. Due to the discovery of Chimney sweeper’s cancer, a new classification of cancers underneath occupational cancers arose; with correlations between certain jobs and cancer being demonstrated. The prominent example in living memory is the positive correlation between smoking and lung cancer. Numerous papers, past 7 and present 8, have shed light to this relationship. Those living in the same household as a smoker have a higher occurrence of lung cancer as well due to second hand smoking effects 9. Second hand smoking has directly caused the death of 2.5 million people between 1964-2014 according the US general surgeon 10. Yet despite this compelling evidence people do still decide to smoke. Chemicals inside the cigarettes which cause havoc in the genetic material are called mutagens, derived from the word mutation. This occurs due to a single gene being mutated but could also arise due to an accumulation of mutations on multiple genes leading to total loss of cellular control, leading to cancer. On the other end of the spectrum leading particular lifestyles has been shown to decrease rates of cancer. One may make the argument that a certain group of individuals more susceptible to cancer may just be behaving differently to the rest of the population, so it is not necessarily the external factor causing the cancer. However, this can be falsified; cancer rates among second generation Japanese Hawaiians, i.e. parents moved from Japan to Hawaii, are similar to the Caucasian population 11. Prostate and breast cancer rates are significantly higher than in Japan, whereas the rates of stomach cancer are lower. This data set also compares between the same generation but those who did not immigrate, and it shows a clear discrepancy; therefore, this discrepancy cannot be due to underlying genetic factors leaving the environment as a prime candidate. It has been shown that some cancers can be controlled by environmental factors. Notable cases include the BRCA1 and BRCA2 genes which produce tumour suppressor proteins by repairing damaged DNA. Without these proteins, the probability a female may develop breast or ovarian cancer at a much earlier age due to the genetic alterations is significantly higher 12. Even with one faulty allele, the effects can be pronounced. Breast cancer, in particular, has been given much attention in the media due to the efforts of actor Angelina Jolie has undergone a double breast mastectomy. Bibliography 10 American Lung Association, 2017. ''Health Effects of Second Hand Smoking. ''Online Available at: https://www.lung.org/stop-smoking/smoking-facts/health-effects-of-secondhand-smoke.html 12 November 2018. 7 Doll, R. & Hill, A. B., 1956. Lung Cancer and Other Causes of Death in Relation to Smoking. ''The British Medical Journal, ''2(5001), pp. 1071-1081. 3 Ellis, H., Calne, R. & Waston, C., 2011. ''Lecture Notes: General Surgery. ''12 ed. s.l.:Wiley-Blackwell. 9 Hirayama, T., 1981. Non-smoking wives of heavy smokers have a higher risk of lung cancer: a study from Japan.. ''The British Medical Journal, ''p. 282. 12 National Cancer Institute, 2018. ''BRCA mutations: Cancer Risk and Genetic Testing. ''Online Available at: https://www.cancer.gov/about-cancer/causes-prevention/genetics/brca-fact-sheet 24 October 2018. 8 Peto, R. et al., 2000. Smoking, smoking cessation, and lung cancer in the UK since 1950: combination of national statistics with two case-control studies. ''British Medical Journal, ''pp. 321-323. 4,5,6 Waldron, H. A., 1983. A brief history of scrotal cancer. ''British Journal of Industiral Medicine, ''4(40), pp. 390-401. 1,2,11 Weinberg, R. A., 2014. ''The Biology of Cancer. ''2nd Edition ed. s.l.:Garland Science. Category:Bibliography